Semiconductor image sensors are used to sense radiation such as light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are widely used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels in a substrate, including photodiodes and transistors, that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals.
A back side illuminated (BSI) image sensor device is one type of image sensor device. These BSI image sensor devices are operable to detect light projected from its backside. A BSI image sensor device has a relatively thin silicon substrate (e.g., a few microns thick) in which light-sensing pixels are formed. The thin nature of the silicon substrate makes the pixels more susceptible to variations in stress, which may be caused by various backend processes and different pattern designs. Stress on the silicon substrate may increase leakage current, and the variations in stress may make leakage current calculations more difficult.
Hence, while existing BSI image sensor devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.